The examination of respiratory tract tissue via fiberoptic bronchoscopy is a well-established technology, and its limitations are also known. For example, if a lesion is peripheral it may not be clear, even with fluoroscopy, whether a biopsy is obtained from the abnormality itself or from nearby non-representative tissue. Because the bronchoscope cannot reach beyond the fourth order bronchi, the diagnostic yield of peripheral masses by current methods of bronchoscopic biopsy is significantly lower than obtained in central lesions.
Fiberoptic brochoscopy was introduced in the late 1960s to allow direct visualization of the tracheobronchial tree. Ikeda, S., "Flexible broncho-fiberoscopy," Ann Otol Rhinol Laryngol, 79, 916-923 (1970); Shure, D., "Fiberoptic Bronchoscopy: diagnostic applications," Clin Chest Med, 8, 1-13 (1987). With this modality, it is possible to detect abnormalities of the tracheobronchial tree, including intraand extraluminal masses, acute and chronic inflammation, and lymphadenopathy. Bronchoscopic signs of disease, including mural deformity and fixation as well as endoluminal obstruction, are used to determine the site for biopsy in order to obtain tissue either directly from the area of suspected primary disease or from involved lymph nodes.
Aided by standard chest radiography, computed tomography, and fluoroscopy during bronchoscopy, it is currently possible to further localize extraluminal tumor or lymph nodes that are amenable to transbronchial biopsy, but, in spite of radiographic guidance and visible deformity, the precise location of extraluminal masses or lymph nodes viewed through the bronchoscope may not be apparent. It is also usually not possible to identify major pulmonary and mediastinal blood vessels, let alone separate arterial from venous structures. If a tumor is necrotic, the preferred site for biopsy may be at the periphery of the lesion and not identifiable with either fluoroscopy or fiberoptic bronchoscopy. If the lesion is peripheral, it may not be clear even with fluoroscopy whether a biopsy specimen is obtained from the abnormality itself or from nearby nonrepresentative tissue.
Since its introduction, fiberoptic bronchoscopy has evolved into one for the most common procedures for the diagnosis of pulmonary disease. Improvements in bronchoscopic optics and imaging acquisition technology as well as in the tissue sampling capabilities of the procedure have expanded its applications, resulting in an overall positive yield of over 90% in cases of obstructing carcinoma. At the same time, as noted above, the limitations of transbronchoscopic biopsy are well recognized. It is often difficult to achieve positive results in cases of necrotic tumors or small peripheral submucosal or peribronchial neoplasms. Tracheal lesions are often difficult to sample accurately because of the angle of the biopsy needle in relation to the tracheal wall. The diagnostic yield of peripheral masses at bronchoscopy is considerably lower than that of central endobronchial lesions, with reported yields of transbronchial biopsy and brushing in the range of 30%-60%. Small peripheral lesions 3 cm or less in diameter are particularly difficult to characterize with fiberoptic transbronchial biopsy, in part because only one or two bronchi traverse lesions of this size. However, three or more bronchi may be encompassed by larger lesions, increasing the chance that the bronchoscopic forceps or needle will locate the correct site for biopsy.
Supplementary imaging techniques have been helpful in increasing the yield of fiberoptic bronchoscopy in both central and peripheral lesions. Biplane or C-arm fluoroscopy has been particularly useful in increasing the diagnostic yield of the bronchoscopic procedure by demonstrating the location of the forceps or needle in the region of the mass. Pre-procedural planning with high resolution or conventional computed tomography also aids in establishing an appropriate bronchoscopic approach.
In peripheral lesions, fluoroscopy clearly shows the relationship of the tip of the bronchoscope to the mass in the anterior-posterior projection. However, the intubated bronchus may actually lie in front of or behind the mass, and, as a result, the biopsy may not yield positive results. Although computed tomography with 5-mm sections through the mediastinum clearly demonstrates the bronchial anatomy in relation to the suspected mass, it is difficult to precisely duplicate the relationship of the mass, nodes, and vessels--particularly in the case of extraluminal masses.
Thus, it would be desirable to be able to more specifically locate a lesion or other site under study. It would also be desirable to provide methods and apparatus such that upon location, a biopsy could be performed at the site. Therefore, it is an object of the present invention to provide improved methods and apparatus for visualizing the tissue within a patient, and in particular tissue in the tracheobronchial tree. It is another object of the present invention to provide improved methods and apparatus for taking a biopsy.
Thoracic ultrasound has been used for the study of masses and other abnormalities of the chest wall, pleura, lung parenchyma, and mediastinum, the incompatible size of conventional ultrasound transducers compared with the diameter of the biopsy channel of the standard adult-size bronchoscope precluded its use in the past. Saito, T., et al., "Ultrasonographic approach to diagnosis of chest wall tumors," Chest, 94, 1271-1273 (1988); Izumi, S., et al., "Ultrasonically-guided aspiration needle biopsy in diseases of the chest," Am Rev Respir Dis, 125, 460-464 (1982).
Miniature catheter-based ultrasound transducers with a diameter of 3.5 to 6.2 French have been used in conjunction with flexible endoscopy of the genitourinary and gastrointestinal tracts because of their ability to image beyond the luminal surface, providing information about the exact location of masses as well as such normal structures as arteries, veins, and lymph nodes. Goldberg, B. B., et al., "Sonographically guided laparoscopy and mediastinoscopy using miniature catheter based transducers," J Ultrasound Med 12, 49-54 (1993); Liu, J. B., et al., "Transnasal US of the esophagus: preliminary morphologic and function studies," Radiology, 184, 721-727 (1992).